The invention relates to imaging, and specific embodiments of the invention relate more particularly to projecting stationary images onto a moving object.
In various industries employing photo-lithography, there is a desire to use two-dimensional light valves to project images onto moving objects. One typical use for such image projection involves projecting a UV image in order to expose a UV sensitive material, such as photoresist or photopolymer. One advantage of two-dimensional light valves (as compared to lasers) is that low brightness sources, such as arc lamps, can be used with light valves. The best known device using a light valve to project an image is the video projector, which is commonly used to project video and computer generated images onto a screen. Prior art systems for projecting images onto moving objects use one of the following methods:
a) Using a step-and-repeat technique, wherein the object is stepped over a certain movement and then is held stationary at the moment of imaging. The stepping and imaging may then be repeated a number of times to complete the image;
b) Synchronizing the image to the motion of the object by shifting the data in the light valve. See, for example, U.S. Pat. Nos. 5,049,901; 5,208,818; and 5,132,723.
c) Moving both the light valve and the object at the same time. See, for example U.S. Pat. Nos. 5,870,176 and 6,060,224;
d) Dividing the image into columns and using an acousto-optic modulator to synchronize the image with the motion one column at a time. See, for example, U.S. Pat. Nos. RE37,376E and 5,923,359.
None of these techniques involve using a stationary light valve based projector to project a series of stationary images in a rapid sequence to image a continuously moving object.
The invention uses a scanning device between an image source, typically a commercial video projector, and a moving object, typically a planar object which may be coated with photoresist. The scanning device allows the projector and the projected image to remain stationary while the scanning device tracks the motion of the moving object until one frame is exposed. At the end of each frame the scanning device resets to the initial position while the image source changes the image to the next frame. The process repeats itself until a complete stripe of images is recorded. For imaging in the UV, the video projector lamp and the optics may be modified in order to enhance the UV output. After one stripe of images is recorded, further stripes may be imaged using a conventional two-dimensional scanning method. Either stepping motion or continuous helical motion can be used to scan the second dimension of the object.
The invention allows the use of a low cost, off-the-shelf video projector as a lithographic imaging device, without requiring step-and-repeat type motion of the object or the imaging source. One advantage of a continuous mechanical motion over a stepped motion is in a smoother, more accurate and more reliable mechanical system. The present invention is particularly useful in the following applications: the production of printing plates (both lithographic and flexographic), the production of printed circuit boards (also known as xe2x80x9cdirect imagingxe2x80x9d), the production of displays and the production of solid objects from photonolymer.